1. Field of the Invention
The present invention relates to medical devices. In particular, the present invention relates to clinical chemistry analyzers which are used for the measurement of medically significant substances in body fluids.
2. Description of the Prior Art
The increasing sophistication in the treatment of disease in recent years has led to the need for diagnostic instrumentation that will effectively gather accurate information on the patient before treatment begins. A critical component of this information gathering involves blood analysis for determining the presence and concentration of particular chemicals in the blood.
The methods by which chemical data are gathered for accurate medical diagnosis constitute a branch of medical science called clinical chemistry. Currently there are three major methods which are commonly used to measure the level of chemicals in blood or other body fluids. These methods are: optical, flame photometry, and ion selective electrodes.
The optical methods (which are sometimes referred to as spectrophotometric methods) operate on the principle that when specific reagents are mixed with a sample of the body fluid, a reaction takes place which allows the measurement of the chemical of interest by measuring the change in wavelength of light transmitted by the sample. The clinical chemistry analyzer systems which use an optical method have typically operated by either mixing the sample with a prepackaged amount of reagents or by allowing the mixing of the sample with the reagents through various tubing and mixing operations.
In flame photometry methods, the sample is consumed in a flame. The specific light produced by a given chemical of interest during the combustion process is used to determine the level of that chemical in the body fluid.
Ion selective electrode measurement methods use electrodes having membranes that selectively interact with chemical ions of interest. These methods involve a potentiometric, amperometric or other electrical measurement which is a function of the concentration of the ion of interest in the sample.
In the past, the clinical chemistry analyzers using optical, flame photometry or ion selective electrode methods have tended to be large in size, expensive, and complex to operate. Analyzers using optical techniques or ion selective electrodes have been expensive to acquire due to the complexity of the mechanical systems and the nature of the exacting measurement required. They have also needed trained operators to continually monitor and evaluate the measurements, have required exhaustive and frequent maintenance, and have required frequent calibration.
Analyzers using flame photometry have also required trained operators and an extremely high amount of maintenance. In addition, flame photometers have required a source of propane and an open flame, which is undesireable for safety reasons.
In general, only large medical institutions have been able to afford the purchase of clinical chemistry analyzers. Smaller hospitals, clinics and physician group practices usually have had to employ centralized hospital laboratories or commercial laboratories to do their chemical tests. These laboratories have grown substantially in the last decade with the increased emphasis on measurement of medically significant substances in the blood and other body fluids as a part of the physician's diagnosis prior to treatment.
In the past, basic blood chemistry tests have often been very time consuming. When a physician has required a basic blood test, a blood sample has been taken and sent to a laboratory for analysis. The results of the test in nonemergency cases has taken from one hour to several days. In the meantime, the patient may have left the clinic and then had to return later or be telephoned to consult with the physician on the results of the test. This procedure has been inconvenient and medically inefficient for both the physician and the patient.
There is a strong need for clinical chemistry instrumentation that can be readily available to all physicians who desire to conduct selected basic chemistry tests without delay and at a reasonable cost. This need extends to individual doctor's offices, physician group praactices, hospitals for bedside applications, operating and emergency rooms, cardiac and intensive care units, nursing homes, ambulances and emergency vehicles, and in centralized laboratories for immediate ("stat") use.
This need for improved clinical chemistry instrumentation, however, requires an analyzer which is less expensive to acquire, is easier to operate, requires less maintenance, eliminates the need for an open flame, eliminates the need for constant manual calibration and verification of measurements, reduces drift effects to a negligible level, eliminates need for handling of calibrated reagents, is portable enough to allow its use where required, and uses whole blood so that the time consuming step of centrifuging blood samples is eliminated, and requires very small volumes of blood for testing. The prior art clinical chemistry analyzers, however, have been unable to meet all of these requirements.